Thermally stable fuels and stabilizing agents therefor



United States Patent 3 269 808 THERMALLY STABLE FliELS AND STABILIZING AGENTS THEREFOR Arthur V. Churchill, Oakmont, Arvid Ek, Shaler Township, Allegheny County, and Elizabeth L. Fareri, Pittsburgh, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Aug. 7, 1961, Ser. No. 129,554

4 Claims. (Cl. 4462) absorbed heat developed in the engine by compression of combustion air, by fuel combustion, and by friction of moving parts. As a result, the fuel is subjected during service to heat transfer surface temperatures of the order of 300 to 400 F. or more for relatively substantial time intervals. In addition, the fuel may be subjected to even higher temperatures, of the order of 500 F. or higher, for short periods of time in the vicinity of the nozzles or orifices through which the fuel is introduced into the combustion chamber of the engine in which the fuel is being consumed. As a result of exposure to these high temperatures, certain components of the fuel tend to undergo decomposition due to polymerization, oxidation, and thermal degradation, and to form solid or semi-solid degradation products that clog the fuel orifices and that foul heat transfer surfaces and thereby interfere with proper combustion of the fuel and proper operation of the engine. Ordinary stabilizing agents, antioxidants, and the like of the kind that .are employed tostabilize the fuels during storage have been found inadequate to inhibit decomposition of the fuels at temperatures of the magnitude encountered in the vicinity of the combustion chamber, fuel orifices, and the heat transfer surfaces of aviation turbine engines, thus indicating a difference in kind between low or moderate temperature deposits, that is, deposits formed below 300 F. and the high temperature deposits with which the present invention is concerned.

The present invention relates to improving the thermal stability of liquid hydrocarbon distillate fuels boiling in the combustion gas turbine fuel range, such as aviation turbine fuels, and to reducing the tendencies of such fuels to form deposits on heat transfer surfaces at temperatures in excess of 350 F. and in the fuel inlet regions of the combustion zones of the engines in which the fuels are consumed, whereby such fuels are rendered more suitable for use in these engines. It has been found that the thermal stability characteristics of these fuels can be im proved by incorporating therein a small amount of a combination of '(I) an N,N-di(orthohydroxyarylmethylidene) allrylenepolyamine that contains 2 to 3 amino groups and whose alkylene groups contain 2 to 6 carbon atoms each, such as N,N-disalicylidene-1,2-propylenediaamine, and (II) and oil-soluble sulfur-containing polymer of .a monomeric alkylmercaptoalkyl ester of a polymeriza- 3 269,808 Patented August 30, 1966 able alpha,beta-ethylenic monocarboxylic acid whose alkylmercaptoall yl groups contain 3 to 30 carbon atoms, said polymer containing an average of at least 9, preferably at least 10, side-chain hydrocarbon substituent carbon atoms for each monomeric unit present in the polymer. Excellent results are obtainable with polymers of alkylmercaptoalkyl esters of lower alpha,beta-ethylenic acids, such as acrylic and lower alpha-alkacr-ylic acids Whose alkylmercaptoalkyl groups contain 4 to 15 carbon atoms, such as beta-dodecylmercaptoethyl methacrylate and betaisooctylmercaptoethyl methacrylate, but other materials of the class can be used with good results. It is not necessary that all of the side-chain hydrocarbon substituent carbon atoms of the sulfur-containing polymer be present in the alkylmercaptoalkyl snbstituents, as the invention also includes the use of copolymers of the above-described monomers with sulfur-free monomers or other comonomers that contain a copolymerizable ethylenic linkage and that contain a hydrocarbon substituent in a side-chain. A portion of the average number of side-chain hydrocarbon substituent carbon atoms required for the purposes of the present invention, that is, any number from 1 to 27, preferably 8 to 18, can be present in the hydrocarbon substituents of the side-chains of the comonomers. An example of a preferred sul'fur free comonomer from which the sulfurcontaining copolymers disclosed herein can be derived is lauryl methacrylate, but other comonomers having a cop-olymerizable ethylenic linkage and that have a hydrocarbon substituent in a side-chain can be used. Examples of such other materials are octyl acrylate, oleyl methacrylate, lauryl crotonate, isooctylaminoethyl methacrylate, diisooctylaminoethyl methacrylate, vinyl stearate, vinylphenyl oleate, vinyl octyl ether, vinyl lauryl ether, alpha-eicosene, alpha-tetradecene, or mixtures of any of these sulfur-free monomers. When the sulfurcontaining monomer is utilized in the form of a copolymer, the sulfur-containing monomer should be present in the copolymer in a weight ratio with respect to the comonomer or cornonomers in the range of at least about 0.03:1, and preferably 0.05:1 to 0.75:1. Oil-soluble, sulfur-containing polymers of the class disclosed herein containing at least 0.03 percent by weight of the hereindisclosed sulfuncontaining monomers will normally be characterized by a sulfur content of about 0.2 to 15 percent sulfur by weight. Copolymers containing about 1.3 to 3.5 percent sulfur have been found to produce excellent results for the purposes of this invention and are therefore preferred, but polymers containing greater or lesser amounts of sulfur can be used. Specific examples of oilsoluble sulfur-containing polymers whose use is included by the present invention are the homopolymer of betadodecylmercaptoethyl methacrylate, the 1:9 weight ratio copolymer of beta-ethylmercaptoethyl methacrylate and lauryl methacrylate, the 2:8 weight ratio copolymer of beta-ethylmercaptoethyl methacrylate and lauryl methacrylate, the 1:9 weight ratio copolymer of betamethylrnercaptoethyl methacrylate and lauryl methacrylate, and the 121:8 weight ratio ter'polymer of beta-ethylmercaptoethyl methacrylate, beta-diis0o ctylaminoethyl methacrylate and lauryl methacrylate, but other oil-soluble, sulfur-containing copolymers of the class disclosed herein can also be used. The herein-disclosed oil-soluble, sulfur-containing polymers can be employed in conjunction with N,N- di(orthohydr-oxyarylmethylidene) alkylenepolyamines in varying proportions with respect to one another. It is generally preferred to add both materials to the hydrocarbon fuels in about equal proportions by weight, but other proportions, say in the range of 1:10 to 1, can be used provided that the compound present in the smaller amount is present in an amount corresponding to at least about 2.5 pounds per thousand barrels of fuel. Proportions in the range of 10 to pounds per 1,000 barrels of hydrocarbon fuel are preferred for each of the respective components of the combination, but other proportions, ranging up to as much as 50 pounds or more per thousand barrels of fuel, can be used. Although the oil-soluble, sulfurcontaining polymers disclosed herein are employed in conjunction with the herein-disclosed N,N'-di(orthohydroxyarylmethylidene) alkylenepolyamines when it is desired to minimize both heat transfer surface deposits and combustion chamber fuel inlet deposits, and when the base fuel is unstable in both respects, the oil-soluble, sulfurcontaining polymers can also be employed as such either in fuels that already have satisfactory resistance to formation of thermal deposits on heat transfer surfaces either when uninhibited or when inhibited with other heat transfer surface deposit inhibitors than the N,N'-di(orthohydroxyarylmethylidene) alkylenepolyamines disclosed herein that do not interfere with the thermally stabilizing properties of the sulfur-containing polymers, and the present invention includes fuels stabilized in this fashion. The present invention further includes the combination of additives disclosed herein, apart from the fuels to which they are added.

The exact mechanism by which the compounds disclosed herein function to improve the thermal stability of hydrocarbon fuel has not been definitely established. Nevertheless, available experimental data clearly indicate that the respective classes of compounds disclosed herein coact with one another, as it has been found that not every combination of the herein-disclosed oil-soluble sulfur-containing polymers and materials-other than the herein-disclosed N,N'-di(orthohydroxyarylmethylidene) alkylenepolyamines-that alone will effect a reduction in heat transfer surface deposits, will effect a reduction in both heat transfer surface deposits and combustion chamber inlet deposits.

The oilsoluble sulfur-containing copolymers disclosed herein can be prepared in any convenient way. For ex ample, they can be prepared, as described in copending application Serial No. 129,551, filed August 7, 1961, by causing the desired sulfur-containing monomer or a mixture thereof to react with the desired comonomers in the Weight ratios disclosed in the presence of a diluent, preferably a solvent, such as toluene, benzene, ethyl acetate or other solvents having similar chain transfer activity, at a temperature in the range of -75 C. to 150 C., preferably C. to 150 C., in the presence of a few hundredths percent to two percent, preferably 0.2 to 1.0 percent, of a catalyst for free radical reactions such as benzoyl peroxide, lauroyl peroxide, or alpha,alpha'-azodiisobutyronitrile, preferably in the substantial absence of oxygen, for about minutes to hours, or until the rate of formation of larger polymer molecules has declined substantially. The latter limit is determinable by periodic sampling of the reaction mixture and observing for a decline in the rate of increase in the viscosity of the polymeric product. Alternatively, instead of the polymerization procedure described above, conventional bulk or dispersion polymerization methods can be used as can other conventional polymerization catalysts. The sulfurcontaining monomers referred to above, in turn, are best prepared as described and claimed in copending applica; tion Serial No. 129,503, filed August 7, 1961, by transesterification of an alkylmercaptoalkanol with a lower alkyl ester of the desired polymerizable alpha,beta-unsaturated monocar boxylic acid, in the presence of a suitable polymerization inhibitor and a suitable transesterification catalyst.

Insofar as the orthohydroxyarylmethylidene-substituted alkylenepolyamine component of the combination improvement agent disclosed herein is concerned, we prefer to employ those members whose orthohydroxyaryl substituents are either unsubstituted or substituted only with hydrocarbon substituents, but orthohydroxy-arylmethylidene-substituted alkylenepolyamines that are substituted with other groups such as alkoxy, halo, cyano, and carboxy groups can be used. As indicated, the preferred orthohydroxyarylmethylidene-substituted alkylenepolyamine for purposes of this invention is N,N'-disalicylidene 1,2 propylenediamine. Examples of other N,N di(orthohydroxyarylmethylidene) .alkylenepolyamines are N,N' di(2 hydroxy 6 methylbenzylidene) 2,3 butylenediamine, N,N' di(orthohydroxynaphthylidene) 1,3 propylenediamine, N,N' di(2- hydroxy 3 methoxybenzylidene) 3,4 diaminohexane, N,N' di(2 hydroxy 5 chlorobenzylidene)- 1,2 propylenediamine, N,N' di(2 hydroxy 3 cyanobenzylidene)-ethylenediamine, N,N' di(2 hydroxy 3 carboxybenzylidene)-ethylenediamine and N,N' disalicylidenediethylenetriamine.

Sulfur-containing monomers capable of forming sulfurcontaining polymers that are useful for the purposes of the present invention include a wide variety of alkylmercaptoalkyl esters of polymerizable :alpha,beta-unsaturated monocarboxylic acids whose alky-lmercaptoalkyl substituents contain 3 to 30 carbon atoms. When the sulfur-containing polymer is a homopolymer, the sulfur-containing monomer from which the polymer is derived should itself contain a total of at least 9, preferably at least 10, side-chain hydrocarbon substituent carbon atoms to insure oil-solubility of the homopolymer. Specific examples of such monomers are beta-dodecylmercaptoethyl methacrylate and beta-isooctylmercaptoethyl methacrylate. Examples of other sulfur-containing monomers are l2-dodecylmercaptododecyl, gammadocosylmercaptopropyl and beta-octacosylmercaptoethyl esters of acrylic or lower alpha-alkacrylic acid such as methacrylic acid or other lower polymerizable aplha,betaunsaturated monocarboxylic acids such as crotonic, angelic, .tiglic, and senecioic acids. When the desired sulfur-containing polymer is a copolymer, the sulfur-containing monomer can be any member of the class whose side-chain hydro-carbon substituent carbon atoms, together with the side-chain hydrocarbon substituent carbon atoms in the comonomer or comonomers, average at least nine, and preferably ten, side-chain hydrocarbon substituent carbon atoms per monomeric unit in the copolymer. Specific examples of monomers that will form oil-soluble copolymers useful for the purposes of the herein-disclosed invention are beta-methylmercaptoethyl methacrylate, beta-ethylmercaptoethyl methacrylate and beta-dodecylmercaptoethyl methacrylate. Examples of other monomers capable of forming copolymers whose use is included by the present invention are the betapropylmercaptoethyl, gamma ethylmercaptopropyl, beta hexylmercaptoethyl, l2 dodecylmercaptododecyl and beta-octadecylmercaptoethyl esters of acrylic acid or lower alpha-alkacrylic acid such as methacrylic acid or other copolymerizable lower alpha,beta-unsaturated monocarboxylic acids such as crotonic, angelic, tiglic, and senecioic acids.

When the sulfur-containing polymer is a copolymer of a sulfur-containing monomer and a comonomer, the comonomer can be any suitable monomeric material or mixture of monomers containing a copolymerizable ethylenic linkage and containing a side-chain hydro-carbon substituent containing 1 to 27, preferably 8 to 18, carbon atoms. Excellent copolymers for the purposes of the present invention are obtainable from higher fatty esters of acrylic or lower alpha-alkacrylic acids, of which lauryl methacrylate is a preferred example. The expression higher fatty esters, is used in its usual sense to indicate an aliphatic hydrocarbon substitutent containing 8 or more carbon atoms. Specific examples of other sulfur-free monomers useful in the preparation of the herein-described copolymers include other long-chain saturated and unsaturated esters of acrylic or lower alphaalkacrylic acid or other co-polymerizable lower alpha, beta-unsaturated monocarboxylic acids, particularly those acids containing 3 to 5 carbon atoms, such as octyl acrylate, oleyl methacrylate, and lauryl crotonate. Still other copolymerizable sulfur-free ethylenically unsaturated monomers that are useful in the preparation of the herein-described copolymers include esters of ethylenically unsaturated alcohols and long-chain fatty acids such as vinyl stearate, vinylphenyl oleate, unsaturated ethers such :as vinyl octyl ether and vinyl lauryl ether, and mono-olefinic olefin polymers such as alpha-eicosene and alpha-tetradecene.

The side-chain hydro-carbon substituents of the monomers can be linked to the polymerizable portion of the monomer through other than a carbon to carbon linkage. For example, such substituents can be linked to the polymerizable portion of the monomer through linkages involving oxygen, nitrogen, sulfur, and/ or phosphorus, as for example in the case of esters, ethers, or the like. Especially effective copolymers are obtainable from nitrogeneous monomers containing an ethylenic linkage that is coplymerizable with the ethylenic linkage of the sulfur-containing monomeric components and containing an organic nitrogen-containing substituent group. The organic nitrogen-containing substituent groups are characterized by the presence of at least one hydrocarbon N-substituent containing 1 to 18, preferably 8 to 18 carbon atoms. The organic nitrogen-containing substituent group can be associated with the copolymerizable portion of the nitrogenous monomer molecule in various Ways. For example, the substituents can be linked to the monomer chain through an ester linkage or in other ways as by salt linkages, including both quaternary ammonium salt and addition salt linkages, as Well as those involving dehydrated addition salt, that is, amido, link ages. Specific examples of preferred nitrogenous monomers are isooctylaminoethyl methacrylate and diisooctylaminoethyl methacrylate.

The herein-described copolymers can be derived not only from the sulfur-containing monomers and the sulfurfree monomers described above but also from one or more additional monomeric compounds copolymerizable therewith that may or may not contribute to the oil solubilityor thermal stability-promoting properties of the copolymers, provided that the proportions of such additional monomeric compounds are so restricted as not to diminish significantly the desired minimum oil-solubility and thermal stabilizing properties of the copolymers. Examples of such compounds include ethylenically unsaturated copolymerizable monomers such as vinyl, allyl, and crotyl acetates, butyrates, and the like, ethylene, propylene, isobutylene, styrene, 1,3-butadiene, acrylic acid, acrylonitrile or the like.

The average molecular weight of the copolymers disclosed herein will normally be greater than about 2,000 and preferably greater than about 7,500, as determined by conventional methods. Usually the average molecular weight of the copolymers will not exceed about 500,000 but the molecular weights can be greater, provided they are not so large as to render the polymers insoluble in the liquid hydrocarbon fuel distillates disclosed herein.

The herein-described sulfur-containing thermally stabilizing compositions can be incorporated i the liquid hydrocarbon fuels disclosed herein in any suitable manner. For example, they can be added to the fuel singly or in combination either as such or in diluted form promptly after distillation of the fuel or after storage at normal atmospheric temperatures for an indefinite period of time. Alternatively, the sulfur-containing thermally stabilizing compositions disclosed herein can be added to the fuels in admixture with other addition agents adapted to improve one or more characteristics of the fuels. For example, the thermally stabilizing compositions disclosed herein can be added to the fuels in admixture with corrosion inhibitors or conventional antioxidants.

The sulfur-containing thermally stabilizing compositions disclosed herein can be employed in hydrocarbon distillate fuels that are to be subjected to temperatures above 300 F. in any proportion sufi'icient to improve the thermal stability of the latter. The effective proportions of the respective components of the thermally stabilizing combinations described herein may vary somewhat from member to member of the respective classes and also in accordance with the thermal stability of the uninhibited fuel. A noticeable improvement in thermal stability often will be obtained by the use of as little as 2.5 pounds of each component stabilizer of the stabilizing mixture per thousand barrels of fuel, but it is usually desirable to employ at least five pounds of each component per thousand barrels of fuel in order to obtain a substantial improvement in thermal stability. A major improvement will ordinarily be obtained by the use of the respective components in proportions in the range of about 10 to 20 pounds per thousand barrels of fuel. Although it is not usually necessary to exceed proportions of 20 pounds of each component per thousand barrels of fuel, the respective components of the herein-described thermally stabilizing compositions can be employed in greater proportions, for example, up to 50 pounds or more per thousand barrels of fuel, in instances of fuels having unusually poor thermal stability characteristics, or extreme service temperatures.

Hydrocarbon fuels of the kind Whose use is included by this invention are normally liquid hydrocarbon distillate mixtures boiling in the combustion gas turbine fuel range, such as ordianry aviation turbine fuels, that is, jet fuels. The properties of the most common aviation turbine fuels are defined fully in the following specifications: MIL-J-S 161E (Referee JP4 Fuel), MIL-J5624D (JP- 4, JP- 5 Fuel), MIL-F-25656 (JP-6 Fuel), MIL-F- 25524A (Thermally Stable Fuel), MIL-F-25558B (RI-1 Fuel), MILR25576B (RP-l Fuel), and ASTM D1655 59T. In general, aviation turbine fuels are characterized by the following common properties:

Gravity, API 32.5-57.

Existent gum, mg./ ml. (max.) 5-7.

Potential gum, mg./100 ml. (max.) 4-14.

Sulfur, percent (max.) 0.5-0.4.

Mercaptan sulfur, percent (max.) 0.0010.005.

Freezing point, F. (max.) -75 to 40.

Thermal value, B.t.u./lb. (min.) l8,300l8,500.

Aniline, gravity constant 4,500, usually Aromatics, vol. percent (max.) 5-25.

Olefins, vol. percent (max.) a. 1-5.

In addition to these characteristics, it also may be noted that typical aviation turbine fuels employed for use in aviation turbine engines involving a high temperature fuel stability problem normally boil in the range of about 250 to 700 F., that is to say, these aviation turbine fuels normally boil above the gasoline range. Although the invention is especially effective in the thermal stabilization of aviation turbine fuels that are subjected during use to high service temperatures, it is also useful in stabilizing hydrocarbon fuels of comparable boiling ranges during high temperature processing operations so as to reduce fouling of heat exchanger tubes, and the invention includes such use.

The ability of the materials disclosed herein to reduce formation of thermal deposits in distillate hydrocarbon fuels at high service temperatures has been demonstrated by subjecting representative fuel compositions of the kind disclosed herein to the CFR Fuel Coker t'est procedure. This test procedure is described in detail in the Manual of ASTM Standards on Pertoleum Products, ASTM Dl66059T. In accordance with this test method, aviation turbine fuels are subjected to flow conditions and temperature stresses similar to those in combustion gas turbine or jet aircraft engines by circulation through a simulated aircraft fuel system at a temperature above 300 F., at a rate of six pounds of fuel per hour, for a period of 300 minutes. The test apparatus comprises a fuel system containing two heated sections, one of which is a preheater section that simulates the hot fuel line sections of an aviation turbine engine as typified by the engine fuel-lubricating oil cooler. The extent of fouling of heat transfer surfaces in the preheater section by fuel degradation deposits is determined by inspection, and the extent of such fouling is used as one index of the high temperature stability of the aviation turbine fuel in the heat exchanger section of an aviation turbine engine Preheater deposits are rated according to the following scale: =no visible deposits; 1=haze or dulling, but no visible color; 2=barely visible coloration; 3=lighter tan to peacock stain; 4=heavier than 3.

The second heated section comprises a filter section that simulates the nozzle area or fuel inlet area of the combustion zone of a jet engine where fuel degradation particles may be trapped. A precision, sintered stainless steel filter is employed in the filter section to trap fuel degradation particles formed during the test. The extent of the buildup of fuel degradation particles in the filter section is indicated by the pressure differential across the test filter, and this pressure differential is used as another index of the high temperature stability of the aviation turbine fuel. In carrying out the tests described, the temperature of the fuel at the outlet of the preheater section was maintained at 400 F., except where otherwise indicated, and the filter section temperature was maintained at 500 F.

In the specific embodiments described herein the polymers tested are identified, respectively, as Polymers A, B, C, D, and E. Polymer A was a lubricating oil solution of a 1:9 weight ration copolymer of beta-ethylmercaptoethyl methacrylate and lauryl methacrylate prepared by causing 450 grams of beta-ethylmercaptoethyl methacrylate and 4,050 grams (4,700 ml.) of lauryl methacrylate to react in the presence of 27 grams alpha,alpl1a'-azodiisobutylronitrile as a catalyst in 9,000 grams (10.4 liters) of toluene as a reaction solvent, at 65 C. for about six hours, with nitrogen bubbling through the reaction mixture and stirring throughout the reaction. Solvent was removed by evaporation under reduced pressure when the reaction was complete. The residue was then blended with an equal weight (4,500 g.) of a hydrocarbon oil of lubricating grade as a solvent for the polymer. The sulfur-containing monomer in turn was prepared by causing 2,233 grams of ethylmercaptoethanol to react with 4,156 grams of methyl methacrylate in the presence of 80 grams of tetrabutyl titanate as a transesterification catalyst and 40 grams of paraethoxyphenol as a polymerization inhibitor, in a glass vessel with moderate heating. Nitrogen was bubbled through the reaction mixture throughout the reaction. An azeotrope of methyl alcohol and methyl methacrylate was distilled off at atmospheric pressure. When this fraction had been completely distilled, excess methyl methacrylate was distilled at 80 mm. Hg at 40 C. This fraction was followed by a small fraction boiling up to 95 C. at mm. Hg. Bet-a-ethylmercaptoethyl methacrylate was then distilled off at a temperature of 96 to 100 C. at 10 mm. Hg. Analysis of a polymeric product prepared by the method described above was as follows:

Sulfur, percent 0.79

Average molecular wt., shear method 1 65,000

Bueche and Hardin", Journal of Pol mer Sclen e, vol.

XXXII, pages 177-186 (1958). y C

Polymer B was a lubricating oil solution of a 2:8 weight ratio copolymer of bet'a-ethylmercaptoethyl unethacrylate and *laury-l methacrylate prepared by causing 100 grams of beta-ethylmercaptoethyl methacrylate and 400 grams of lauryl methacrylate to react in the presence of three grams of alpha,alpha-azodiisobutyronitrile in 1,000 grams of toluene as a reaction solvent, at 65 C., for about six hours, with nitrogen being bubbled through the reaction mixture and with stirring throughout. The reaction mixture was then distilled under vacuum to remove solvent, the temperature being carried to C. at 2 mm. Hg to remove the last traces of solvent. The remaining polymer was then blended with 500 grams of a 10W/20 hydrocarbon oil of lubricating grade to form a 50 percent solution of the polymer.

Polymer C was a lubricating oil solution of a 111:8 Weight ratio terpolymer of beta-ethylmercaptoethyl methacrylate, diisooctylaminoethyl methacrylate and lauryl methacrylate prepared from 50 grams of beta-ethylmercaptoethyl methacrylate, 50 grams of diisooctylaminoethyl methacrylate, 400 grams of lauryl methacrylate, 3 grams of alpha,alpha-azodiisobutyronitrile and 1,000 grams of an SAE IO-grade lubricating oil as a solvent for the reaction product. The method of preparation was the same as that used in the preparation of Polymer B except that with the direct use of a lubricating oil reaction solvent there was no need for intermediate solvent removal at the close of the reaction period.

Polymer D was a 1:9 weight ratio copolymer of methylmercaptoethyl methacrylate and lauryl methacrylate prepared similarly as Polymer C from 30 grams of betamethylmercaptoethyl methacrylate, 270 grams of lauryl methacrylate, 1.8 grams of alpha,al pha azodiisobutyronitrile and 600 grams of an SAE 10W lubricating oil.

Polymer E was a homopolymer of beta-dodecylmercaptoethyl methacrylate prepared similarly as Polymer C from 250 grams of n-dodecylmercaptoethyl methacrylate, 1.5 grams of the alpha,alpha-azodiisobutyronitrile and 500 grams of an SAE 10W lubricating oil.

In the tests described herein the test fuels, hereinafter referred to, respectively, as Aviation Turbine Fuel 1, Aviation Turbine Fuel 2, and Aviation Turbine Fuel 3, were commercial-type aviation turbine fuels having the following characteristics:

Aviation Aviation Aviation Turbine Turbine Turbine Fuel 1 uel 2 Fuel 3 Gravity, API 43.3 43.6 44.3 Freezing Point, F-.. 60.0 53 .0 56.0 Sulfur, L, percent 0.058 0.055 0.064 Mercaptan Sulfur, percent 0.001 0.001 0.001 Existent Gum, rug/ rnl 0.5 1 .1 1 .0 Potential Gum, nag/100 m1 1.6 3 .1 3.0 Aromatics, vol. percent. 16 .2 15 .9 14.0 Olefins, vol. percent-.- 1 .5 1 .2 0.9 saturates, vol. percent- 82 .3 82. 85.1 Thermal Value, B t u llb- 18, 576 18, 578 Anilme-Gravity Constant 6, 3 6, 364 6, 539 Distillation, Kerosene:

Over Point F--- 335 330 338 End Point, F- 532 532 526 10% Evap. at 368 364 374 50% Evap. at 418 416 421 90% Evap. at 486 476 479 The make-up of the test samples and the results obtained in tests carried out with respect to a thermally Table A Fuel 1 Reference Fuel 2 Reference 1 2 3 Ie Maximum Rating Average Rating-- From a comparison of the test results obtained in the respective test runs indicated in the preceding table, it will be seen that the herein-described copolymers as such exert a marked reduction in thermal filter deposits as evidenced by virtual elimination of a pressure drop across the filter, although the particular polymer tested, in conjunction with Test Fuel 1, tended slightly to promote preheater deposits. On the other hand, the N,N'-disalicylidene-1,2-propylenediamine completely inhibited deposits in the preheater section, while at the same time tending to promote filter deposits. In Run 3 the additive combination of Polymer A and N,N'-disalicylidene-1,2- propylenediamine completely eliminated filter deposits as well as preheater deposits. Thus, each component of the combination thermal stabilizing composition not only functioned similarly as when used separately but in addition modified the undesirable side effects of the other component. The fuel composition employed in Run 3 is a specific embodiment of a preferred fuel composition of this invention. The 1:1 weight ratio stabilizer mixture employed in the test fuel of Run 3, prior to addition to the fuel, is a specific example of a stabilizer mixture subcombination as such. The fuel employed in Run 2 is a specific example of a sulfur-containing polymer-fuel subcombination.

The effectiveness of other sulfur-containing polymers whose use is included by the present invention was shown by subjecting fuel compositions prepared from Aviation Turbine Fuel 3 and Polymers B, C, D, and E to the above-described test procedure. The results of these tests are set forth in Table B, below.

Table B Fuel 3 1 2 3 4 Reference Make-up; percent by vol.:

Aviation Turbine Fuel 3 100 100 100 100 100 Polymer Added, lbs/1000 bbls. (Active): Polymer B Polymer C Polymer D Polymer E Inspections:

OFR Fuel Coker Test- Filter Section, 500 F: Time to Reach a Pressure Drop 0110 in. Hg,

IlllIl *75 300 300 300 300 Time to Reach a Pressure Drop of 25 in. Hg,

min 300 300 300 300 Pressure Drop at 300 min., in. Hg 25 0.10 0.10 0.10 1. 60

Preheater Section,

410 F.-Preheater Deposits (0 Perfect): Maximum Rating *4 4 3 4 4 Average Rating "1. 75 1.6 1.0 2.0 1.8

*Average of two determinations.

Comparison of the test results obtained in Runs 1, 2, 3, and 4 with the results obtained with the reference fuel shows that in every case a marked reduction in filter deposits was obtained. Comparison of the results obtained in Test Runs 1 and 2 with those obtained with the reference fuel indicate that a slight and a marked reduction in preheater deposits, respectively, are also obtained by Polymers B and C.

It will be understood that the invention is not limited to the particular sulfur-containing polymers or N,N- di(orthohydroxyarylmethylidene) alkylenepolyamine described in the preceding specific embodiments, and that other materials disclosed herein can also be employed with good results. For example, there can be substituted for the polymers of the preceding specific embodiments in the same or equivalent proportion any of the 0.05:1, the 0.1:1, and the 0.5 :1 weight ratio copolymers of betaethylmercaptoethyl acrylate and crotonate with lauryl acrylate and crotonate, and homopolymers of beta-dodecylmercaptoethyl and 12-dodecylmercaptododecyl acrylates and crotonates. Similarly, for the N,N-disalicylidene-1,2-propylenediamine of the preceding specific embodiment there can be substituted in the same or equivalent proportions any of N,N'-di(2-hydroxy-6- methylbenzylidene)-2,3-butylenediamine, N,N-di(orthohydroxynaphthylidene) 1,3 propylenediamine, N, N- di(2 hydroxy-3-methoxybenzylidene) 3,4 diaminohexane, N,N'-di(2-hydroxy-3-cyanobenzylidene) ethylenediamine, N,N-di(2 hydroxy-3-carboxybenzylidene) ethylenediamine, and N,N'-disalicylidenediethylenetriamine.

The hydrocarbon fuel compositions of this invention can also contain various other addition agents adapted to improve one or more properties of the fuel. For example, these compositions can contain in addition to the polymers disclosed herein, corrosion inhibitors, freezing point depressants, antioxidants, metal deactivators, combustion and/ or ignition improvement agents and the like. When additional control of heat transfer surface deposits is desired, the fuel compositions of this invention can also contain supplemental preheater deposit inhibitors.

Many modifications and variations of the invention as herein-described will suggest themselves to those skilled in the art, and resort may be had to such modifications and variations without departing from the spirit and scope of the invention. Accordingly, only such limitations should be imposed as are indicated in the claims appended hereto.

We claim:

1. A fuel composition comprising a major amount of a normally thermally unstable, normally liquid hydrocarbon mixture boiling in the aviation turbine fuel range and a small amount, sufficient to improve the thermal stability of said fuel composition of a combination of (I) N,N-disalicylidene-1,2-propylenediamine, and (II) an oil-soluble sulfur-containing 1:9 Weight ratio copolymer of monomeric beta-ethylmercaptoethyl methacrylate and lauryl methacrylate, said small amount corresponding to at least 2.5 pounds of each of said N,N-disalicylidene- 1,2-propylenediamine and said oil-soluble sulfur-containing copolymer per thousand barrels of fuel.

2. A fuel composition comprising a major amount of a normally thermally unstable, normally liquid hydrocarbon mixture boiling in the aviation turbine fuel range and a small amount, sufficient to improve the thermal stability of said fuel composition of an oil-soluble sulfur-containing 1:9 weight ratio copolymer of beta-ethylruercaptoethyl methacrylate and lauryl methacrylate.

3. A fuel composition comprising a major amount of a normally thermally unstable, normally liquid hydrocarbon mixture boiling in the aviation turbine fuel range and a small amount, sufiicient to improve the thermal stability of said fuel composition of an oil-soluble sulfurcontaining 2:8 Weight ratio copolymer of beta-ethylmercaptoethyl methacrylate and lauryl methacrylate.

4. A thermal stabilizer combination capable of coacting to reduce both heat transfer surface deposits and combustion chamber inlet deposits in normally thermally unstable, normally liquid hydrocarbon mixtures boiling in the aviation turbine fuel range, comprising approximately equal proportions by weight of N,N'-disalicylidene-1,2- propylenediamine and a 1:9 Weight ratio copolymer of beta-ethylmercaptoethyl methacrylate and lauryl methacrylate.

References Cited by the Examiner UNITED STATES PATENTS 2,800,450 7/1957 Bondi et a1. 4462 2,800,453 7/1957 Bondi et al. 44-72 2,925,406 2/ 1960 McCurdy et a1. 260486 2,974,025 3/ 1961 Ertelt et al. 4471 3,034,876 5/1962 Gee et a1. 44-62 3,067,019 12/1962 Churchill et a1 44-62 3,102,863 9/1963 Herbert et al. 252-48.6 X

FOREIGN PATENTS 776,955 6/ 1957 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

M. WEINBLATT, C. O. THOMAS, J. E. DEMPSEY,

Y. M. HARRIS, Assistant Examiners. 

1. A FUEL COMPOSITION COMPRISING A MAJOR AMOUNT OF A NORMALLY THERMALLY UNSTABLE, NORMALLY LIQUID HYDROCARBON MIXTURE BOILING IN THE AVIATION TURBINE FUEL RANGE AND A SMALL AMOUNT, SUFFICIENT TO IMPROVE THE THERMAL STABILITY OF SAID FUEL COMPOSITION OF A COMBINATION OF (I) N,N''-DISALICYLIDENE-1,2-PROPYLENEDIAMINE, AND (II) AN OIL-SOLUBLE SULFUR-CONTAINING 1:9 WEIGHT RATIO COPOLYMER OF MONOMERIC BETA-ETHYLMERCAPTOETHYL METHACRYLATE AND LAURYL METHACRYLATE, SAID SMALL AMOUNT CORRESPONDING TO AT LEAST 2.5 POUNDS OF EACH OF SAID N,N''-DISALICYLIDENE1,2-PROPYLENEDIAMINE AND SAID OIL-SOLUBLE SULFUR-CONTAINING COPOLYMER PER THOUSAND BARRELS OF FUEL. 